The present disclosure is directed to a continuous tow fiber coating reactor which may be used in a system for coating tow fibers and to a method for coating the tow fibers using the reactor.
Fiber reinforced ceramic matrix composite (CMC) materials are finding a greater number of applications in high temperature oxidizing environments due to their material properties including, but not limited to, high temperature and oxidation resistance, high strength and creep resistance, high thermal conductivity and low weight. One of the CMC materials considered for aerospace applications is the SiC fiber/SiC matrix CMC material in which unidirectional SiC fibers with a thin layer of boron nitride (BN) interface coating (typically less than 1.0 μm thick) are imbedded in a SiC matrix.
An advantage of CMC materials compared to their corresponding monolithic materials is that such materials are significantly tough even though their constituents may be intrinsically brittle. This feature is achieved by utilizing an appropriate fiber/matrix interface coating(s), such as BN, that arrest and deflect cracks formed under load in the brittle matrix and prevent early failure. Furthermore, the interface coatings protect the fibers from detrimental interactions with each other, with the matrix, and with the environment in the CMC component application(s). Therefore, interface coatings play an important role in the performance and lifetime of CMC materials during their applications.
Boron nitride has potential as an interface coating material because it has low shear strength and good oxidation resistance capability. A typical process to perform BN interface coatings on SiC fiber tows is through chemical vapor deposition (CVD) via either a continuous tow coating or a batch process. In the continuous tow process, a single tow or multiple tows is/are pulled through a cylindrical or slot shaped BN CVD reactor where the reactants are fed into the reactor via co-feed or counter feed mode with respect to the tow travel direction, achieving the interface coatings on the tows.
An issue in the continuous tow interface coating process is that there is lack of a means to enhance the reactant distribution and associated mass transfer between the filaments and the reactants inside the reactor. Some have used disruptors attached to an inner wall of a single tube reactor to disturb reactant flow inside the reactor to enhance the mass transfer. Despite this, there remains a need to enhance the mass transfer so as to improve interface coatings on the fibers.